I asking for some help!

I am looking for some research help. :???: What I am looking for is all the types and configuations of assist trailers and tagalongs. From the beginnings of the idea back in the late 1800's to now, whats out there. There is so many flavors and ideas I just would like to see and hear as many as possible. This for an article I am writing. Pictures would be great. Please Email me and when I am done I will share the article with you all.